Field of the Invention and Related Art Statement
This invention relates to high strength, high modulus carbon fiber filament yarns and to a method for producing the same. More particularly, it relates to filament yarns of high strength, high modulus carbon fibers, having a fold structure (sometimes known as wrinkled layers) in the fiber cross-section, which do not form the well-ordered three dimensional structure unique to polycrystalline graphite and to a method for producing the same as a crack-free filament from a specified pitch by using specified spinning nozzles under specified conditions.
Materials prepared by a combination of special materials are required in many industries to produce products having high strength and high Young's modulus, together with light weight
Among the most promising materials to be used are resins, reinforced with high strength, high modulus carbon fibers. When the carbon fibers are combined with a resin, it is possible to produce reinforced resins capable of exhibiting characteristic features unparalleled in the past. In spite of the high strength and high modulus of the carbon fibers for the above-mentioned reinforced resins, the applications of these fibers have not greatly expanded due to the high production cost.
The high strength, high modulus carbon fibers which are commercially available include polyacrylonitrile-based fibers (hereinafter PAN fibers) produced by special production processes and a special spinning process but these fibers are not only expensive as a precursor of carbon fibers but also, the production yield thereof from the precursor is as low as less than 45%. These facts complicate the treatment steps and enlarge production facilities for producing superior carbon fibers, resulting in very high production cost of the ultimate products using carbon fibers. The production cost of high strength, high modulus carbon fibers of the ultimate product is further increased by the treatment and disposal cost for the hydrocyanic acid by-product generated at the time of carbonization treatment.
Several alternative materials are known from which carbon fibers can be produced. For example, carbon fibers have been obtained by the pyrolysis of cotton, rayon, PVC and PVA fibers [Otani, Carbon 3, 31, (1965)]. Vapor grown fibers have been reported.
One material which is used as an alternative to PAN is mesophase pitch. A term "mesophase" herein referred to is one of the components constituting the pitch and it means an optically anisotropic part of a coal or petroleum base pitch which shines brilliantly when the section of a lump of pitch solidified at a temperature close to room temperature is polished and observed through the crossed nicholas of a reflection type polarizing microscopy. A pitch mostly composed of mesophase is called mesophase pitch. The content of mesophase in, a mesophase pitch is calculated from the percentage of the area of optically anisotropic part obtained by observation under a reflection type polarizing microscope.